Meanwhile, number of injured rose to 29 in the fifth terrorist attack this year, which Prime Minister Theresa May said was 'clearly intended to cause significant harm'.
The United Kingdom's terror threat level was raised to critical, which means an attack is imminent, hours after the explosion.
'The bombing on a metro in London was carried out by a detachment of the Islamic State,' it said in a statement published by its Amaq propaganda agency.
The explosion, on a District Line Tube in the British capital's southwest, occurred as the train pulled into Parsons Green station.
Commuters said they heard a bang and saw a fireball inside the carriage when the 'bucket bomb' exploded.
Several people suffered facial burns, some reportedly were even trampled in the rush to escape.
But none of the injuries were life threatening.
Pictures of a white bucket on fire inside a supermarket bag, with wires trailing on to the carriage floor of the train went viral on social media. -- PTI
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